1. Field of the Invention
The present invention relates to a portable terminal such as mobile phone, PHS (Personal Handyphone System) phone, etc. for performing radio communication with a base station.
2. Description of the Related Art
In recent years, mobile phones and PHS phones have explosively prevailed.
These mobile phones, PHS phones, etc. (hereinafter represented by “mobile phone”) generally have liquid crystal display (LCD) screens and operation panels on which plural operation buttons are arranged. Also, in recent years, models with larger LCD screens have appeared.
A mobile phone generally has a chargeable secondary battery and operates by obtaining electric power from the secondary battery. It is needless to say that the electric power obtained from the secondary battery is used for performing communication using the mobile phone. But also, the obtained electric power is used for lighting up an LCD screen and operation buttons. Such lighting up requires a lot of electric power.
As an important factor to decide performance of a mobile phone, how a mobile phone can operate for a long time after charging until the next charging can be pointed out.
Generally, when any of operation buttons is pressed, both an LCD screen and a pressed operation button are lighted up and it is possible to confirm contents displayed on the LCD screen and operate the operation buttons in a dark place. However, there is also a model in which it is possible to set that operation buttons are not lighted up in order to save the power.
However, if it is set that operation buttons are not lighted up, a user needs to operate buttons mostly by touching them in the dark. Thus, even though such setting saves the power, operability becomes very poor. On the other hand, if it is set that the operation buttons are lighted up attaching importance to operability, the power is wasted.